Schottky diode with minimal vertical current flow

ABSTRACT

A method of forming a rectifying diode. The method comprises providing a first semiconductor region of a first conductivity type and having a first dopant concentration and forming a second semiconductor region in the first semiconductor region. The second semiconductor region has the first conductivity type and having a second dopant concentration greater than the first dopant concentration. The method also comprises forming a conductive contact to the first semiconductor region and forming a conductive contact to the second semiconductor region. The rectifying diode comprises a current path, and the path comprises: (i) the conductive contact to the first semiconductor region; (ii) the first semiconductor region; (iii) the second semiconductor region; and (iv) the conductive contact to the second semiconductor region. The second semiconductor region does not extend to a layer buried relative to the first semiconductor region.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No.11/173,695, entitled “Spike Implanted Schottky Diode,” filed on the samedate as the present application, and hereby incorporated herein byreference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

BACKGROUND OF THE INVENTION

The present embodiments relate to semiconductor circuits and are moreparticularly directed to a Schottky diode with minimal vertical currentflow.

Semiconductor devices are prevalent in all aspects of electroniccircuits, and such circuits use numerous types of elements includingtransistors. Due to the dominance of transistors in many designs, thencircuit method flows are often developed toward constructing thetransistors. However, other circuit elements are preferably implementedas part of the same steps as the transistor method flow, or in a lessdesirable case in some instances an additional step or steps to thetransistor method flow are required to also construct other types ofcircuit elements.

Consistent with the above, another known semiconductor circuit elementis a Schottky diode. A Schottky diode typically includes a metal tolightly-doped semiconductor interface, where this interface is known tohave rectifying characteristics. In many applications, the semiconductorportion at this interface is created using an N type material becausethe resulting diode has a larger barrier height than if a P typesemiconductor is used, and in many applications the larger barrierheight is desirable. However, in some applications it may be desirableto have the lower barrier height as provided by a P type materialincluded in a Schottky diode. For example, one such application is theimplementation of radio frequency identification (“RFID”) devices. Apassive RFID tag device, as known in that art, is a device that has nointernal energy source. It receives a radio frequency (“RF”) signal andprovides a corresponding current in response to that signal. In someapplications, the RFID device will receive a relatively small RF signaland, hence, in these applications a low-barrier Schottky diode isdesirable so as to be operable to sufficiently detect the small RFsignal. In other more general applications, a disadvantage, however, mayarise in low-barrier Schottky diodes in that there may be a dominance ofseries resistance that may cause a relatively large amount of currentflow at low voltage and such current also will be affected by the seriesresistance. In these latter cases, therefore, the use of an N typesemiconductor Schottky diode may be preferred. In any event, therefore,one skilled in the art will appreciate applications for either N type orP type semiconductor Schottky diodes.

By way of further background, semiconductor Schottky diodes have beenconstructed and used in the prior art and in the general form of thecross-sectional illustration of FIG. 1 a, which depicts a diode 10.Diode 10 is formed in connection with a semiconductor substrate 12,which in the example of FIG. 1 a is a P type semiconductor material andwhich is lightly-doped, as shown by the conventional designation of “P−”in FIG. 1 for such type and level of doping. For sake of explanationhere and later contrast to the preferred embodiments, the majority axisof substrate is shown by way of a dashed line and indicated as 12 _(A)and in the illustration is generally horizontal. A layer of N typematerial is formed such as an N well 14 generally above or as part ofthe top portion of substrate 12, and it is lightly-doped as shown by theconventional designation of “N−” in FIG. 1 for such type and level ofdoping. Separating at least a portion of substrate 12 from N well 14 isa buried layer 16, which is N type and heavily-doped as shown by theconventional designation of “N+” in FIG. 1 for such type and level ofdoping. Note that the descriptor “buried layer” is just one of variousterms used in the art, so as to describe a portion of semiconductormaterial that is beneath the surface of an overlying layer; thus, in theexample of FIG. 1, buried layer 16 is beneath the surface 14 _(S) of theoverlying layer of N well 14. A buried layer such as buried layer 16 maybe formed in various fashions, such as by forming it in substrate 12prior to forming an overlying layer or, alternatively, by using a highenergy implantation process that is able to penetrate surface 14 _(S)and form the layer deeper than that surface so that some unaffected anddifferent doped level of material (e.g. N type for well 14) is leftabove the buried layer implant and without the dopant concentration ofthat buried layer. A heavily-doped conductive region 18 is formed fromsurface 14 _(S) down to, and of the same conductivity type as, buriedlayer 16; region 18 also may be referred to by various terms such as asinker and thus hereinafter this region is referred to as sinker 18. Inthe present example where buried layer 16 is N+ material, then so issinker 18. Lastly, diode 10 includes two metal-silicide regions 20 and22. Metal-silicide region 20 is formed over and in contact with sinker18, and metal-silcide region 22 is formed along surface 14 _(S). Notethat diode 10 may include other regions or portions, but they are notillustrated so as to simplify the illustration while permitting a focuson various noteworthy aspects.

The operability of diode 10 is now discussed in connection with FIG. 1b, which again depicts diode 10 but includes a few additionalillustrated aspects. As introduced earlier, a metal to lightly-dopedsemiconductor interface provides rectifying characteristics; thus, indiode 10, the interface of metal-silicide region 22 to N well 14 createssuch characteristics. Thus, in operation, this interface performs akinto a PN junction, so a positive forward bias voltage may be applied tometal-silcide region 22 relative to metal silicide region 20. With thisbias, current flows from metal-silicide region 22 to N well 14, as shownin FIG. 1 b by the generally vertical dashed arrows in N well 14. Thus,with respect to this current flow, it generally is vertical and notparallel to the lateral (or horizontal) majority axis 12 _(A) ofsubstrate 12. Also in this regard, therefore, metal-silicide region 22operates as the diode anode, providing the direction of inward currentflow. Further, the relatively lower potential at metal-silicide region20 is connected through an ohmic connection to the relatively highdoping of sinker 18, which further connects that potential to buriedlayer 16; thus, the current flow continues from N well 14 through buriedlayer 16 and sinker 18 toward metal silcide region 20, therebypermitting the latter to be referred to as the diode cathode. Given thepreceding, it is observed now, and by way of contrast to the preferredembodiments detailed later, that the prior art diode 10 includes aconsiderable vertical component in the direction of its current flow.This vertical component occurs due to the inclusion and use of buriedlayer 16 as part of the diode's conductive path, whereby verticalcurrent flow is facilitated both through well 14 to buried layer 16 andfrom buried layer 16 through sinker 18.

While diode 10 has proven usable and beneficial in variousimplementations, the present inventors have recognized that it may havecertain drawbacks in some circuits. For example, some method flows maynot include a buried layer of the configuration as shown in FIGS. 1 aand 1 b. For example, there may be no buried layer or, alternatively,the buried layer may be of a relatively low doping so as not to providea low resistance connection to the overlying region (e.g., N well 14).Thus, in these examples, including an appropriate buried layer in orderto support a diode would require additional fabrication steps, and oftensuch additions are either undesirable or infeasible due toconsiderations of time, cost, and still other considerations.

In view of the above, there arises a need to address the drawbacks ofthe prior art, as is achieved by the preferred embodiments describedbelow.

BRIEF SUMMARY OF THE INVENTION

In the preferred embodiment, there is a method of forming a rectifyingdiode. The method comprises providing a first semiconductor region of afirst conductivity type and having a first dopant concentration andforming a second semiconductor region in the first semiconductor region.The second semiconductor region has the first conductivity type andhaving a second dopant concentration greater than the first dopantconcentration. The method also comprises forming a conductive contact tothe first semiconductor region and forming a conductive contact to thesecond semiconductor region. The rectifying diode comprises a currentpath, and the path comprises: (i) the conductive contact to the firstsemiconductor region; (ii) the first semiconductor region; (iii) thesecond semiconductor region; and (iv) the conductive contact to thesecond semiconductor region. The second semiconductor region does notextend to a layer buried relative to the first semiconductor region.

Other aspects are also disclosed and claimed.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 a illustrates a cross-sectional view of a prior art diode 10.

FIG. 1 b illustrates the cross-sectional view of the prior art diode 10with an indication of the current flow during operation.

FIG. 2 a illustrates a cross-sectional view of two active regions of asemiconductor structure after certain method flow steps according to thepreferred embodiments.

FIG. 2 b illustrates a cross-sectional view of FIG. 2 a subjected to adopant implant.

FIG. 2 c illustrates a cross-sectional view of FIG. 2 b following theremoval of a mask, the formation of an insulating layer, and theformation of an additional mask.

FIG. 2 d illustrates a cross-sectional view of FIG. 2 c following theetch of the insulating layer and the formation of a metal layer.

FIG. 2 e illustrates a cross-sectional view of FIG. 2 d followingsilicidization of the metal layer and removal of the non-silicidedmetal.

FIG. 3 illustrates a flow chart method 100 of forming the integratedcircuit device of FIGS. 2 a through 2 e.

FIG. 4 illustrates a cross-sectional view of the Schottky diode ofactive region 32 from FIG. 2 d and its operation.

FIG. 5 a illustrates a cross-sectional view of an interdigitatedSchottky diode according to the preferred embodiments.

FIG. 5 b illustrates a plan view of the interdigitated Schottky diode ofFIG. 5 a.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 a and 1 b were described above in the Background Of TheInvention section of this document and the reader is assumed familiarwith the principles of that discussion.

FIGS. 2 a through 2 e illustrate a cross-sectional view of asemiconductor structure 25 according to the preferred embodiments. Forsake of example, note that structure 25 includes a region 30 that may bea substrate, or alternatively, region 30 may be an isolated well that isdisposed over a separate and underlying substrate that is notspecifically shown in the Figures. In the present example, region 30 isa lightly-doped P type material, shown therefore with a “P−”designation. A light doping preferably has a doping profileconcentration on the order of 10¹⁶/cm³ or less. The majority axis ofregion 30 is shown by way of a dashed line as 30 _(A) and in theillustration is generally lateral or horizontal. The direction of axis30 _(A) provides a reference direction and dimension for sake ofdiscussion later in terms of the operation and flow of current for aSchottky diode that is formed in an active region 32 (sometimes referredto as a device region) of structure 25, as will be described in theremainder of this document. By way of further introduction, FIG. 3illustrates a flowchart of the method 100 steps for forming the statedSchottky diode in active region 32 and is referred to concurrently withthe following discussion of FIGS. 2 a through 2 e. Moreover, forpurposes of demonstrating the formation of the Schottky diode at a sametime as other devices and as part of the method flow of such otherdevices, another active region 34 is shown in relation to structure 25,and by way of example a transistor will be formed in active region 34.Lastly, for the method steps and following illustrations, asemiconductor layer 36 as may be formed as a well by way of example isformed above region 30, and region 30 has a majority axis 36 _(A) thatis parallel to axis 30 _(A). In the present example, semiconductor layer36 is a lightly-doped N type material, shown therefore with an “N−”designation.

Looking then to FIG. 3, method 100 begins with a step 102 which followsvarious front end steps that may be used to form various structuralcomponents of transistors with respect to substrate 25, where by way ofexample such components are shown in active region 34 as discussedbelow. Looking first to step 102, a mask is formed and/or otherwisesemiconductor areas are exposed or provided into which a source/drainimplant may occur. In FIG. 2 a and in active region 32 in this regard, amask is formed by applying a photoresist (“PR”) layer 38 to surface 36_(S) and that layer is thereafter etched to form an opening 40 throughlayer 38. In FIG. 2 a and in active region 34 in this regard, areas 42are exposed with respect to various structures previously formed inconnection with creating a transistor. These previously-formedstructures include a gate 44 separated by a gate insulator 46 from layer36. These structures further include insulating sidewalls 48 formedalong the sidewalls of gate 44, and note that the gate structure thusdescribed is isolated by isolating regions 50. Thus, and as shown below,areas 42 constitute the exposed upper surface 36 _(S) of layer 36 asbetween an insulating sidewall 48 and a respective one of isolatingregions 50, and the upper surface of gate 44 may be exposed for theimplant as well. Given these various structures, method 100 thencontinues from step 102 to step 104.

In step 104, one or more separate high-concentration dopant implantoperations are individually performed in a CMOS example, possibly asingle implant in an application other than CMOS, depending on thedesired conductivity types of the transistors at issue as well as theformation of a structure in active region 32 to be used later as part ofthe conductive path of a Schottky diode. For the sake of simplifying thediscussion and illustration, two different dopant conductivity types areshown in FIG. 2 b. As an example, a first such dopant is implanted atone time into one of region 32 or 34 while masking off the other, whilea second and complementary dopant is implanted at another time into theopposite one of region 32 or 34 while masking off the other. In thepresent example, wherein layer 36 is an N type region, then the dopanttype of the implant into active region 32 is an N type dopant, that is,the dopant is of the same conductivity type as the layer into which thedopant is implanted. Moreover, with a goal of achieving the formation ofvery heavy doped regions (i.e., “N+”) by the implant, the dopingparameters are preferably set so as to achieve an implanted dopingprofile having a concentration on the order of 10¹⁹ to 10²¹/cm³ orgreater. Further, the implant is by way of a high-dose ion implantationof high dose of antimony, arsenic or phosphorus species to form NMOSregions that are typically referred to as source/drain regions becauseat the same time actual transistor source/drain regions may be formed.Further, were the present example an alternative embodiment thatimplements complementary conductivity type structures (i.e.,substituting N for P and vice versa in active region 32), then theimplanted ions may be of boron to form PMOS source/drain regions. In thepresent example, therefore, where layer 36 is N type, then antimony,arsenic or phosphorus may be used to form the resulting source/drainregion(s) in active region 32. Particularly, a source/drain region 52 isformed in active region 32 by way of opening 40 (see FIG. 2 a); as shownbelow, technically this region does not serve as either a source ordrain with respect to a transistor, yet the source/drain terminology ismaintained since it is formed using the same process and at the sametime as may be source/drain regions elsewhere with respect to the samesemiconductor layer 36. Further in this regard and also in step 104, asecond implant may be performed and of an opposite conductivity type,which thereby forms source/drain regions 54 ₁ and 54 ₂ and of thisopposite conductivity type (e.g., P type in this example). Thus, regions54 ₁ and 54 ₂ are self-aligned in areas 42, that is, as between eachrespective gate insulator 48 and a respective isolating region 50. Withthese various structures, method 100 then continues from step 104 tostep 106.

Step 106 of method 100 represents various different actions, yet theyare accumulated in step 106 so as to correspond to the illustrations ofFIG. 2 c. Particularly, as part of step 106, the step 102 implant maskis removed, which recall was illustrated in the form of photoresistlayer 38 in FIGS. 2 a and 2 b. Next and as another part of step 106, aninsulating layer 56 is formed along surface 36 _(S) of layer 36, such asby depositing an oxide, a nitride, or a combination of the two. Next andas yet another part of step 106, a metal openings mask is formed overlayer 56, which in FIG. 2 c is achieved by depositing a photoresistlayer 58, followed by patterning steps comprising of exposure anddevelopment steps. More particularly, photoresist layer 58 is patternedto expose portions of insulating layer 56, that is, windows 60 arecreated through photoresist layer 58 for reasons demonstrated below.With these various structures, method 100 then continues from step 106to step 108.

Step 108 of method 100 also represents various different actions thatare accumulated in a single method step 108 so as to correspond to theillustrations of FIG. 2 d. First, an etch selective to the exposedportions of insulating layer 56 is performed to thereby expose surface36 _(S) in the areas of the etch. Thus, surface 36 _(S) is exposed inactive region 32 at the locations provided by windows 60 (see FIG. 2 c),and at the same time the entirety of insulating layer 56 is exposed and,hence removed from, active region 34. Next in step 108 and as shown inFIG. 2 d, the step 106 mask is removed, which recall in the example ofFIG. 2 c was photoresist layer 58. Finally in step 108, a metal layer 62is deposited over the entirety of the device, thereby covering thestructures of active regions 32 and 34. Metal layer 62 is preferablycobalt, although it may be of various materials such as titanium ornickel, although these latter metals may provide a less desirablemetal/semiconductor interface in certain applications. In any event,note with respect to active region 32, therefore, that metal layer 62contacts an underlying semiconductor material in what were windows 60 ofFIG. 2 c, that is, given the etch through those windows and theconsequent same-location removal of insulating layer 56, then metallayer 62 now contacts semiconductor material in those areas. Note alsowith respect to active region 34 that metal layer 62 contacts anunderlying semiconductor material in locations where there was not anupper surface of insulating material; thus, metal layer 62 contacts theupper surface of both source/drain regions 54 ₁ and 54 ₂ as well as theupper surface of gate 44. With these various structures, method 100 thencontinues from step 108 to step 110.

In step 110, a silicidation is achieved, preferably by subjecting theentire device of FIG. 2 d to a heat anneal cycle, with the result shownin FIG. 2 e. Specifically, as a result of the heat cycle, a silicideregion forms only at locations where metal layer 62 contacts an exposedsilicon or polysilicon region and not, therefore, over regions coveredby an insulator (i.e., dielectric). As a result, silicide regions 64,66, 68 ₁, 68 ₂, and 70 are formed, and note that each of these regionsis self-aligned by way of consumption of the underlying exposed siliconor semiconductor. After the heat treatment any unreacted metal remainingfrom layer 62 is removed, preferably by an etch that is selective onlyto that metal (e.g., cobalt) and not the reacted metal (e.g., cobaltsilicide), thereby leaving structure 25 in the form as shown in FIG. 2e. Lastly, while method 100 then concludes for sake of FIG. 3, note thatvarious additional steps may be performed with respect to structure 25,such as other levels of metal and interconnect, where such other stepsare ascertainable by one skilled in the art.

Having described the construction of structure 25, attention is nowdirected to the operation of a Schottky diode per the preferredembodiments, which is effectively what has been constructed in activeregion 32 and, for sake of illustration, which is therefore repeated inoperational form and in the cross-sectional view of FIG. 4. Here again,a metal to lightly-doped semiconductor interface is created, where inthe example of FIG. 4 that is as between silicide region 64 and thelightly-doped N type layer 36 beneath it. Thus, in operation, thisinterface performs akin to a PN junction, so a positive forward biasvoltage may be applied to metal-silcide region 64 relative to metalsilcide region 66. With this bias, current flows from metal-silicideregion 64 to layer 36, as shown in FIG. 4 by the generally lateral (orhorizontal) dashed arrows in layer 36. Thus, with respect to thiscurrent flow, at least a majority of the current flow is parallel tomajority axis 30 _(A) and majority axis 36 _(A). In other words, in FIG.4 and unlike the prior art, there is not a large amount of current thatis generally vertical and, thus, perpendicular to these majority axes,as was the case in the prior art where current flow is downward to aburied layer that has its own majority axis that is parallel to thesubstrate axis. Further, metal-silicide region 64 operates as the diodeanode, providing the inward direction of current flow. Also, therelatively lower potential at metal-silicide region 66 is connectedthrough an ohmic connection to the relatively high doping ofsource/drain region 52, which further connects that potential to layer36; thus, the current flow continues from layer 36 laterally tosource/drain region 52 and then to metal silicide region 66, therebypermitting the latter to be referred to as the diode cathode. Indeed, inthe preferred embodiment, preferred diode operation is achieved when thedistance between the closest edge of metal-silicide region 64 andsource/drain region 52 is approximately one micron or less.

Given the preceding, it is observed now, and by way of contrast to theprior art, that the preferred embodiment Schottky diode of FIG. 4includes a primarily lateral or horizontal component in the direction ofits current flow, that is, one which is parallel to the major axis ofthe associated substrate that supports the device. Moreover, the currentpath consists of a first metal region (e.g., silicide), a lightly-dopedsemiconductor region of a first conductivity type, a heavily-dopedregion of the same first conductivity type that is isolated from or doesnot extend to a buried layer beneath the lightly-doped semiconductorregion, and a second metal region (e.g., silicide). Thus, the preferredembodiment permits a design engineer or the like to take advantage ofhaving a Schottky diode with very good DC and RF characteristicsavailable, by way of example, on CMOS technology with no suitable buriedlayer available or in deep sub-micron technology (e.g., gate width of0.25 micron or less). If there is no buried layer with the correctpolarity of doping in a given method flow where a Schottky diode is tobe integrated, then a prior art diode such as in FIGS. 1 a and 1 b couldnot be fabricated at all or such a diode would have excessive seriesresistance. In contrast, the preferred embodiment diode may beimplemented in these cases. Moreover, as has been shown, various of thesame method flow steps used in contemporary processes for transistorfabrication may be used without necessitating additional steps into theflow and while still being able to construct the preferred embodimentdiode. Accordingly, the preferred embodiment diode may be integratedinto any submicron or CMOS technology, and possibly others as well,without adding processing costs and complexity to the technology whichotherwise would be added if a buried layer and sinker contact wererequired to be added to those processes.

As an additional illustration of the present inventive scope, FIGS. 5 aand 5 b illustrate a cross-sectional and plan (i.e., top) view,respectively, of another Schottky diode 70 according to the preferredembodiments. In general, diode 70 may be constructed according to thesteps of method 100 described above, with the appropriate formation ofmasks so as to create the various components illustrated in FIGS. 5 aand 5 b. Thus, the level of detail provided above is not restated hereand the reader is assumed familiar with the principles of thatdiscussion. Instead, the following focuses on various other aspects ofdiode 70, demonstrating an interdigitated layout that provides stilladditional benefits over the prior art.

Looking to FIG. 5 a, it illustrates, in cross-sectional form, a region72 that may be a substrate, or alternatively, region 72 may be anisolated well that is disposed over a separate and underlying substratethat is not specifically shown in the Figures. In the present example,region 72 is a lightly-doped N type material, shown therefore with an“N−” designation and with a majority axis 72 _(A). A semiconductor layer74 is formed, as a well by way of example, above region 72 and has amajority axis 74 _(A) that is parallel to axis 72 _(A). In the presentexample, semiconductor layer 74 is a lightly-doped P type material,shown therefore with a “P−” designation. Given the illustrated portionsof region 72 and layer 74, an active region 76 is shown as betweenisolating regions 78 ₁ and 78 ₂, formed along surface 74 _(S) of layer74. Three heavily-doped P type source/drain regions 80 ₁, 80 ₂, and 80 ₃are formed in P type lightly-doped layer 74. An insulating layer isformed and etched, with the remaining portions of that layer shown asinsulating pieces 82 ₁, 82 ₂, 82 ₃, and 82 ₄. Three silicide regions 84₁, 84 ₂, and 84 ₃ are formed, each over and in electrical communicationwith a respective source/drain region 80 ₁, 80 ₂, or 80 ₃, and twosilicide regions 86 ₁ and 86 ₂ preferably from the same metal layer thatforms silicide regions 84 _(x), are formed over and in electricalcommunication with lightly-doped layer 74. Again, preferably thedistance between the closest edge of a metal-silicide region 86 _(x) anda source/drain region 80 _(x) is approximately one micron or less.

Looking to FIG. 5 b, it illustrates a plan view of various of thestructures of diode 70 illustrated in connection with FIG. 5 a, althoughfor sake of simplifying the illustration the perimeter of each sourcedrain region 80 _(x) to the extent it is beyond its overlying silicideregion 84 ₁, 84 ₂, or 84 ₃ is shown by way of a dashed lines whereas inactuality such regions would not be visible from a true top perspectivedue to the adjacent insulating pieces 82 _(x). The length of eachsilicide region 84 _(x) or 86 _(x) spans a distance D₁ shown in they-dimension in FIG. 5 b. Moreover, the overall width of diode 70 spans adistance D₂ shown in the x-dimension in FIG. 5 b and that covers theactive region 76 of the device (i.e., between isolating regions 78 ₁ and78 ₂). In the preferred embodiment D₁ and D₂ are approximately the same(or within 90% of one another) so as to provide an overall structurethat is approximately square in layout form. This preferred layout hasbeen determined to provide beneficial operating performance for diode70. For example, such an approach is optimal to reduce parasiticcapacitance as compared to an approach wherein only a single silicidestrip is used for an anode and a single silicide strip is used for acathode.

In connection with both FIGS. 5 a and 5 b, attention is also directed tothe interdigitated form of the layout and the beneficial operationresulting from it. Specifically, this form is defined in that in FIG. 5b, each combination of a silicide region 84 _(x) and its underlyingsource/drain 80 _(x) is separated by a silicide region 86 _(x) fromanother like combination of a silicide region 84 _(x) and its underlyingsource/drain 80 _(x). For example, the combination of silicide region 84₁ and its underlying source/drain 80 ₁ is separated by silicide region86 ₁ from the combination of silicide region 84 ₂ and its underlyingsource/drain 80 ₂. As the other illustrated example, the combination ofsilcide region 84 ₂ and its underlying source/drain 80 ₂ is separated bysilicide region 86 ₂ from the combination of silicide region 84 ₃ andits underlying source/drain 80 ₃. Returning then to FIG. 5 a, a benefitfrom this interdigitated layout is demonstrated. Specifically, FIG. 5 aalso illustrates the various current flow based on the structure ofdiode 70 by way of dashed arrows in layer 74. In this regard, eachsilicide region 84 _(x) receives a positive bias with respect to eachsilicide region 86 ^(x), thereby providing the former as an anode andthe latter as a cathode. Moreover, as may be seen by way of example withrespect to silcide region 86 ₁ acting as a cathode, it receivesapproximately one-half of its current flow from silicide region 84 ₁ andthe other one-half of its current flow from silicide region 84 ₂.Similarly with respect to silicide region 86 ₂ acting as a cathode, itreceives approximately one-half of is current flow from silicide region84 ₂ and the other one-half of its current flow from silcide region 84₃. As a result of these current flows, then the overall resistance ofdiode 70 is reduced as compared to an approach using a singlenon-interdigitated anode and cathode.

Also in connection with diode 70, note that it shares various benefitswith the embodiment of FIG. 4. For example, at least a majority of thecurrent flow is parallel to majority axis 72 _(A) and majority axis 74_(A). In other words, in FIG. 5 a and unlike the prior art, there is nota large amount of current that is generally vertical and, thus,perpendicular to these majority axes. As another example, each currentpath, either in the forward direction if from silicide to lightly-dopedsemiconductor or in the reverse direction if from silicide toheavily-doped semiconductor, consists of a first metal region (e.g.,silicide), a lightly-doped semiconductor region of a first conductivitytype, a heavily-doped region of the same first conductivity type that isisolated from or does not extend to a buried layer beneath thelightly-doped semiconductor region, and a second metal region (e.g.,silicide). Thus, the additional benefits described above with respect tothe FIG. 4 embodiment are also realized with the embodiment of FIGS. 5 aand 5 b.

From the above, it may be appreciated that the preferred embodimentsprovide a Schottky diode with minimal vertical current flow in that thediode conductive path does not include a buried layer or sinker thereto.Various alternatives have been provided according to preferredembodiments, and still others may be ascertained by one skilled in theart. Indeed, certain of the process parameters described herein may beadjusted by one skilled in the art, steps may be added or re-arranged inorder, and substitutions in some materials also may be made. Further andas shown by examples, the preferred embodiment diode may be constructedwith a P type or N type semiconductor material in the metal tolightly-doped semiconductor interface of the Schottky diode. Indeed,based on considerations such as barrier height, one or the other ofthese types may be selected, such as in a preferable implementationwhich may include the use of one or more Schottky diodes in a radiofrequency identification (“RFID”) tag device. Given the preceding,therefore, one skilled in the art should further appreciate that whilethe present embodiments have been described in detail, varioussubstitutions, modifications or alterations could be made to thedescriptions set forth above without departing from the inventive scope,as is defined by the following claims.

1. A rectifying diode, comprising: first semiconductor region of a firstconductivity type and having a first dopant concentration; a secondsemiconductor region in the first semiconductor region, the secondsemiconductor region having the first conductivity type and having asecond dopant concentration greater than the first dopant concentration;a conductive contact in electrical contact with the first semiconductorregion; and a conductive contact in electrical contact with the secondsemiconductor region; wherein the rectifying diode is operable toconduct along a current path, the current path comprising: theconductive contact to the first semiconductor region; the firstsemiconductor region; the second semiconductor region; and theconductive contact to the second semiconductor region; and whereinneither the first nor second semiconductor region extends to a layerburied relative to the first semiconductor region.
 2. The diode of claim1 wherein the first conductivity type is selected from a groupconsisting of P type and N type.
 3. The diode of claim 2 wherein thediode is part of a CMOS integrated circuit with the first semiconductorregion having the same doping concentration as a well of a CMOStransistor and the second semiconductor region having the same dopingconcentration as a source/drain of a CMOS transistor.
 4. The diode ofclaim 2: wherein the first conductivity type is selected as P type; andwherein the diode is implemented in a radio frequency identificationdevice.
 5. The diode of claim 1 wherein the first dopant concentrationis on the order of 10¹⁶/cm³ or less.
 6. The diode of claim 1 wherein thesecond dopant concentration, is on the order of 10¹⁹ to 10²¹/cm³ orgreater.
 7. The diode of claim 1: wherein the first dopant concentrationis on the order of 10¹⁶/cm³ or less; and wherein the second dopantconcentration is on the order of 10¹⁹ to 10²¹/cm³ or greater.
 8. Thediode of claim 1 wherein a distance between a closest edge of theconductive contact to the first semiconductor region and a closest edgeof the second semiconductor region is approximately one micron or less.9. The diode of claim 1: wherein the second semiconductor region in thefirst semiconductor region comprises one of a plurality of highly-dopedsemiconductor regions in the first semiconductor region; and wherein atleast some of the plurality of highly-doped semiconductor regionsprovide either a source or a drain to a transistor.
 10. The diode ofclaim 1 wherein the conductive contact in electrical contact with thefirst semiconductor region and the conductive contact in electricalcontact with the second semiconductor region comprise one of cobalt,titanium, and molybdenum.
 11. The diode of claim 1: wherein the secondsemiconductor region comprises a plurality of semiconductor regions ofthe second dopant concentration; wherein the conductive contact inelectrical contact with the first semiconductor region comprises one ofa plurality of conductive contacts in electrical contact with the firstsemiconductor region; and wherein the conductive contact in electricalcontact with the second semiconductor region comprises one of aplurality of conductive contacts, each in electrical communication witha respective one of the plurality of semiconductor regions of the seconddopant concentration.
 12. The diode of claim 11 wherein each contact inthe plurality of conductive contacts in electrical contact with thefirst semiconductor region is interdigitated relative to each contact inthe plurality of conductive contacts in electrical communication with arespective one of the plurality of semiconductor regions of the seconddopant concentration.
 13. The diode of claim 12: wherein each conductivecontact in the plurality of conductive contacts in electrical contactwith the first semiconductor region and each conductive contact in theplurality of conductive contacts in electrical communication with arespective one of the plurality of semiconductor regions of the seconddopant concentration spans a first dimension; wherein a width thatencompasses all of the plurality of conductive contacts in electricalcontact with the first semiconductor region and every conductive contactin the plurality of conductive contacts in electrical communication witha respective one of the plurality of semiconductor regions of the seconddopant concentration spans a second dimension; and wherein one of thefirst dimension and the second dimension is within ninety percent of thefirst dimension and the second dimension.
 14. The diode of claim 1wherein the diode is implemented in a radio frequency identificationdevice.
 15. A rectifying diode, comprising: a buried layer of a firstconductivity type residing in a semiconductor body of a secondconductivity type; a first semiconductor region residing above theburied layer in the semiconductor body, the first semiconductor regionnot contacting the buried layer, and having a first conductivity typeand a first dopant concentration; a second semiconductor region in thefirst semiconductor region, the second semiconductor region having afirst conductivity type and a second dopant concentration that isgreater than the first dopant concentration; a conductive anode contacton the first semiconductor region; and a conductive cathode contact onthe second semiconductor region.